Trait Display

1.0.0 · Source

pub trait Display {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}

Expand description

Format trait for an empty format, {}.

Implementing this trait for a type will automatically implement the ToString trait for the type, allowing the usage of the .to_string() method. Prefer implementing the Display trait for a type, rather than ToString.

Display is similar to Debug, but Display is for user-facing output, and so cannot be derived.

For more information on formatters, see the module-level documentation.

§Completeness and parseability

Display for a type might not necessarily be a lossless or complete representation of the type. It may omit internal state, precision, or other information the type does not consider important for user-facing output, as determined by the type. As such, the output of Display might not be possible to parse, and even if it is, the result of parsing might not exactly match the original value.

However, if a type has a lossless Display implementation whose output is meant to be conveniently machine-parseable and not just meant for human consumption, then the type may wish to accept the same format in FromStr, and document that usage. Having both Display and FromStr implementations where the result of Display cannot be parsed with FromStr may surprise users.

§Internationalization

Because a type can only have one Display implementation, it is often preferable to only implement Display when there is a single most “obvious” way that values can be formatted as text. This could mean formatting according to the “invariant” culture and “undefined” locale, or it could mean that the type display is designed for a specific culture/locale, such as developer logs.

If not all values have a justifiably canonical textual format or if you want to support alternative formats not covered by the standard set of possible formatting traits, the most flexible approach is display adapters: methods like str::escape_default or Path::display which create a wrapper implementing Display to output the specific display format.

§Examples

Implementing Display on a type:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.x, self.y)
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");

Required Methods§

1.0.0 · Source

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

§Errors

This function should return Err if, and only if, the provided Formatter returns Err. String formatting is considered an infallible operation; this function only returns a Result because writing to the underlying stream might fail and it must provide a way to propagate the fact that an error has occurred back up the stack.

§Examples

use std::fmt;

struct Position {
    longitude: f32,
    latitude: f32,
}

impl fmt::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}, {})", self.longitude, self.latitude)
    }
}

assert_eq!(
    "(1.987, 2.983)",
    format!("{}", Position { longitude: 1.987, latitude: 2.983, }),
);

Display

Trait Display Copy item path

§Completeness and parseability

§Internationalization

§Examples

Required Methods§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

§Errors

§Examples

Implementors§

impl Display for DivError

impl Display for PositDecodeError

impl Display for amplify_num::hex::Error

impl Display for arbitrary::error::Error

impl Display for ascii::ascii_char::AsciiChar

impl Display for OidParseError

impl Display for asn1_rs::class::Class

impl Display for DerConstraint

impl Display for asn1_rs::error::Error

impl Display for asn1_rs::error::SerializeError

impl Display for async_channel::TryRecvError

impl Display for async_channel::TryRecvError

impl Display for TokioTpErr

impl Display for async_native_tls::acceptor::Error

impl Display for JsonCodecError

impl Display for base16ct::error::Error

impl Display for ParseAlphabetError

impl Display for base64::decode::DecodeError

impl Display for DecodeSliceError

impl Display for EncodeSliceError

impl Display for base64ct::errors::Error

impl Display for bincode::error::ErrorKind

impl Display for PopError

impl Display for const_oid::error::Error

impl Display for GenError

impl Display for DecodeKind

impl Display for der::error::ErrorKind

impl Display for der::tag::class::Class

impl Display for der::tag::Tag

impl Display for TagMode

impl Display for BinaryError

impl Display for DynasmError

impl Display for LabelKind

impl Display for TargetKind

impl Display for equix::err::Error

impl Display for Actual

impl Display for Kind

impl Display for Source

impl Display for fs_mistrust::err::Error

impl Display for CompilerError

impl Display for hashx::err::Error

impl Display for FromHexError

impl Display for httparse::Error

impl Display for humantime::date::Error

impl Display for humantime::duration::Error

impl Display for InvalidStringList

impl Display for icu_collections::codepointtrie::error::Error

impl Display for icu_locale_core::parser::errors::ParseError

impl Display for PreferencesParseError

impl Display for DataErrorKind

impl Display for indexmap::GetDisjointMutError

impl Display for EventMaskParseError

impl Display for liblzma::stream::Error

impl Display for log::Level

impl Display for log::LevelFilter

impl Display for Action

impl Display for TriggerAction

impl Display for DistType

impl Display for maybenot::error::Error

impl Display for Event

impl Display for TriggerEvent

impl Display for PemError

impl Display for pem_rfc7468::error::Error

impl Display for pkcs1::error::Error

impl Display for pkcs8::error::Error

impl Display for postage::stream::errors::TryRecvError

impl Display for rand::distr::bernoulli::BernoulliError

impl Display for rand::distr::uniform::Error

impl Display for rand::distr::weighted::Error

impl Display for rand::distributions::bernoulli::BernoulliError

Trait Display